Here, positional information is understood to mean the position and the alignment of the optical implement with respect to a reference coordinate system, i.e. a coordinate system of a position capturing apparatus. The positional information can be captured by means of a position capturing apparatus with a corresponding measurement system.
In many surgical interventions, the surgeon is faced with the problem of orientation within the patient during the operation. Image data of the patient, e.g. computed tomography recordings, often underlie the planning. During the operation, the medical practitioner works having a direct view onto the operating site. To this end, optical visualization systems/optical implements such as endoscopes or microscopes are available. In order to implement the planning, the medical practitioner needs to create the link between the pre-surgical image data and the intraoperative visual information. As a result of orientation difficulties, this can lead to an extended operation duration or to errors during the operation.
Medical navigation systems are known as orientation aid during the operation. These systems capture the coordinate transforms between the patient and one or more instruments during the operation and visualize these in the pre-surgical planning data. To this end, patient and instrument are equipped with localizers, the position and alignment of which is captured by a measurement system as position capturing apparatus. As measurement systems of a position capturing apparatus, use is made, inter alia, of electromagnetic, optical or ultrasound systems with appropriate sensors, as is also envisaged for the device according to the invention in specific embodiments. The device according to the invention can have an appropriate design. It can comprise appropriate apparatuses for this.
It is known to provide different instruments with localizers for one of such measurement systems, e.g. pointing instruments, suction apparatuses, forceps, needles and the like and to calibrate this instrument such that a coordinate transform to a reference point (generally the instrument tip) is known. The position of the reference point with respect to the anatomy of the patient is displayed on a monitor during the operation in radiological image data of the patient.
Furthermore, in addition to the instruments, which are held directly on a structure, it is also known to provide and calibrate an optical aid, such as an endoscope, with localizers and a device for measuring the distance. As a result, the navigation system captures the position of the endoscope and the device for measuring the distance captures the distance to a structure from a reference point of the endoscope. The combination of the two items of information makes it possible to calculate and present the position of the measurement point, captured contactlessly, in the image data.
It is known that coils with a soft iron core can be used as localizers in electromagnetic measurement systems with alternating fields. Characteristic potential differences are induced into these coils in the alternating field of the so-called field generator of the measurement system, from which characteristic potential differences the position of the coil with respect to the field generator can be established. Since such coils are employed as sensors in an electromagnetic measurement system for capturing the position, they are also referred to as sensor coils.
When presenting the position of the navigated instruments, slice images from a volume data record (e.g. obtained by computed tomography) are often used and the position is plotted into the layer as a point, cross or the like. Three orthogonal planes are often displayed.
As a result of the installation size or as a result of the measurement principle, the known localizers of many measurement systems have to be attached to a part, which remains outside of the patient, of an instrument, the position of which should be captured. As a result, the instrument must have a rigid design in order to ensure an unambiguous transform for the navigation. Hence, it is not possible to navigate flexible instruments using position measuring technology that cannot be attached to the tip of the instrument. Reasons for the attachment outside of the patient may lie in the utilized measurement method, the installation size of the utilized sensor system, insufficient ergonomics by applying the sensor system or a lack of hygiene.